Antibacterials that are used as growth promoters in animal husbandry can affect the release of Shiga-toxin-2-converting bacteriophages and Shiga toxin 2 from Escherichia coli strains

Antibiotics are commonly used as growth promoters in animal husbandry world wide. This practice has been linked to the emergence of particular antibiot ic-resistant bacteria, and is now controversial. In this study, the ability of growth-promoting antibiotics to induce Shiga toxin (Stx)-converting bac teriophages from Stx-producing Escherichia coli (STEC) strains was investig ated. Subinhibitory concentrations of the antibacterial growth promoters ol aquindox, carbadox, tylosin and monensin were used for induction experiment s. The amount of mature Stx-converting phage particles released from induce d and non-induced cultures was determined, and the production of Stx was si multaneously measured by ELISA. Whereas the quinoxaline-1,4-dioxide-type an tibiotics olaquindox and carbadox enhanced the release of Stx-converting ph age particles from STEC cells, tylosin sind monensin decreased phage induct ion. The production of Stx increased or decreased simultaneously with the a mount of free phages. The results of this study show that particular antiba cterial growth promoters can induce Stx phages. In vivo induction of Stx ph ages from lysogenic STEC may increase the amount of free phages in the inte stine and therefore may contribute to the spread of STEC and development of new STEC pathotypes.